For many years there has been a long felt need in the industry to have a lightweight, highly flexible and crush resistant electrically shielded conduit. In response to that need various solutions have been attempted. For example, U.S. Pat. No. 3,466,210 to Wareham in 1966 discloses a method of heat shrinking fibrous material (including electrical shielding material) around the outside of a tubular member or conduit. Others have also attempted to solve the long felt need by similarly wrapping electrically shielded braid over one conduit and sandwiching it with another layer of larger size conduit. For example, one product presently on the market, manufactured by Icore of Sunnyvale, California, comprises a first spiraled or convoluted conduit tubing wrapped with electrical shielding braid, and sandwiched by a second larger cross-section spirally convoluted conduit tubing which is force fit over the braid and first conduit. The Icore structure is quite heavy and loses some of its flexibility as a result of the two layers of conduit tubing.
Others have similarly wrapped the outside surface of the conduit tubing with overlapping layers of electrical shielding, e.g. Plumber, U.S. Pat. Nos. 3,467,761 and Silver, et al 3,651,244. The overlapping layers of electrical shielding causes the shielding layer to be an irregular layer resulting in possible undesirable hoop effects.
Likewise, Silver, et al supra, discloses a shielding tape wrapped over the outside of a conduit. It is presumed that such a conduit does not lose a great deal of its flexibility. However, when one one considers the hoop effects of such wrapped tape and the irregular shielding layer resulting therefrom, the disclosed structure may not be useful in a variety of situations.
Relatively recently, the art of inflexible type shielding conduits has significantly advanced; see for example, McLaughlin, U.S. Pat. Nos. 3,946,143 and 4,016,356 assigned to Raychem Corporation, the assignee herein, which discloses methods for making shielding cable using heat shrinkable technology. It will be noticed that in essence one conduit is again wrapped around the outside of another larger diameter conduit sandwiching the electrical braid between the two conduits.
Applicant has discovered a lightweight, highly flexible, internally and uniformly electrically shielded conduit not disclosed or taught by any of the above mentioned discoveries. The applicant's structure includes an outer flexible tubing layer and internal shielding layer being continuously and continually held against the tubing layer by an internal woven retaining means.